1. Field of the Invention
The present invention relates to a pad assembly for a disc brake, which is assembled in a disc brake of a vehicle, for preventing a noise of braking and uneven wear of a pad.
2. Related Art
In order to prevent a noise of a disc brake and uneven wear of a pad, there is a disc brake in which a shim plate is provided between a claw portion of a caliper and a front end surface of a piston, and the pad. When the claw portion of the caliper and the front end surface of the piston are directly brought into contact with a rear surface of a pressure plate constituting the pad, accompanying the pad which moves in a circumferential direction of a rotor while braking, the caliper has tendency to move in the circumferential direction of the rotor by a frictional force generated between the caliper and the pad. Accordingly, a movement of the caliper becomes in an unstable state, and thus, uneven wear is likely to occur in a lining of the pad in the circumferential direction. When the uneven wear occurs, the pad rapidly reaches a wear threshold or the surface pressure applied between the pad and the rotor becomes uneven in the circumferential direction, so that the noise of a brake can be easily generated.
To prevent the above-described drawbacks, there has been provided with a shim plate made of a sheet of stainless steel plate between the claw portion of the caliper and the front end surface of the piston, and the rear surface of the pressure plate constituting the pad. In addition, there has been designed that locking pieces provided at ends of the shim plate are slidably fixed to an outer periphery of the pressure plate in the circumferential direction of the rotor. By making it easy to relatively displace the caliper and the pad during braking, the movement of the caliper can become stable so that the uneven wear hardly occurs in the pad. However, in the disc brake, if the rear surface of the pressure plate has low roughness precision (rough), it is hard to achieve desired sliding characteristics with respect to the rear surface of the shim plate, and thus the above-described effect cannot be achieved.
In this respect, disclosed in JP-Y-06-011377 is a disc brake, in which a shim plate set 3 made by superimposing a pair of inner and outer shim plates 1 and 2, as shown in FIG. 5, is provided between a claw portion of caliper and a piston, and a rear surface of a pressure plate constituting a pad. In the disc brake of JP-Y-06-011377, both ends in a width direction (right and left side of FIG. 5) of the inner shim plate 2 on the pad side (inner side of FIG. 5), and both ends in the width direction (right and left side of FIG. 5) of the outer shim plate 1 on a counter-pad side (outer side of FIG. 5) are respectively provided with guiding parts 4 and 5. The guiding parts 4 and 5 are bent in a U-shape viewed from a section view, and their opened sides are respectively facing the counter-pad side. While the inner shim plate 2 and the outer shim plate 1 are superimposed on each other, a pair of guiding parts 5 and 5 is disposed at the inner side of a pair of guiding parts 4 and 4 provided at the inner shim plate 2, maintaining a gap in a radial direction of the rotor (top and bottom of FIG. 5) thereby guiding the outer shim plate 1 to move in the circumferential of the rotor with respect to the inner shim plate 2. Further, both ends of the inner shim plate 2 in the radial direction of the rotor (top and bottom of FIG. 5) are provided with a plurality of locking parts 6 and 6 which are bent toward the pad, so that the inner shim plate 2 can be locked with the pressure plate by the locking parts 6 and 6.
In the structure described in JP-Y-06-011377, frictional force to be applied between the inner shim plate 2 and the outer shim plate 1 can be easily made smaller than frictional force applied between the rear surface of the pressure plate and the inner shim plate 2. For this reason, even when the rear surface of the pressure plate has low roughness precision (rough), the movement of the caliper can be made stable by smoothly deviating the caliper and the pad each other while braking. Therefore, it is possible to prevent uneven wear on the pad.
In the structure in JP-Y-06-011377, while the inner shim plate 2 is fixed to the pad by the plurality of locking parts 6 and 6, the outer shim plate 1 is not prevented from moving in an axial direction of the rotor (front and back side of FIG. 5) with respect to the inner shim plate 2. For this reason, the outer shim plate 1 can be easily separated from the pad, and handling and workability for assembling the pad and the shim plate set 3 is difficult prior to mounting to the disc brake. In the structure described in JP-Y-06-011377, the plurality of guiding parts 4 and 5 are provided to guide the outer shim plate 1 in the circumferential direction of the rotor with respect to the inner shim plate 2, and the plurality of locking parts 6 and 6 are provided to have the inner shim plate 2 locked with the pad. Accordingly, the whole structure of the inner and outer shim plates 1 and 2 should have a number of bent parts, and the bent parts are not uniformly bent in one direction, which causes cost to increase.